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Laboratoire : P’ PMM, ENSMA – Poitiers Responsables : Xavier Milhet, Loic Signor, P. Gadaud Financement : MESR |
” EVOLUTION DES PROPRIETES MECANIQUES D’UN MATERIAU NANOPOREUX AU COURS DE SON VIEILLISSEMENT: ESSAIS, CARACTERISATION STRUCTURALE ET MODELISATION “
Nature du travail : numérique / experimental
The need of reducing the emissions of gas responsible for the greenhouse effect has prompted the research for alternative solutions to replace the machines using fossil energy, especially in transportation. However, a rapid increase of electric or hybrid vehicles on the market rely mostly on their dependability such as growing expectations on the reliability of the embedded power electronics for example. In the same time, regulations for the use of harmful materials are becoming more and more restrictive. In this context, this proposal aims at studying alternative materials to lead (Pb) or Pb-based alloys for die bonding.
Various Pb- free solutions are considered in order to face the severe electro-thermo-mechanical constraints applied to the electronic systems. However, these materials can be the weak point of the electronic system on the one hand from there limited thermal and electronic properties and on the other hand, from the build-up of thermal stresses resulting from a difference in coefficient of thermal expansion between the chip and the solder.
Among the different technological solutions, silver (Ag) paste sintering is a good candidate because of the relative simple process to implement at the industrial level and their very high electrical conductivity. Sintering of Ag paste, performed at low pressure (few MPa) and low temperature (up to 280°C approximately) gives a material with a non-negligible residual porosity. Porosity is known to alter the properties of materials compared to its dense state. While the evolutions of the electrical properties and, at a
lesser extent the mechanical properties, are being looked over during aging, no clear relation with the microstructure evolution is reported in the literature. This is an important parameter since starting from an initial homogeneous distribution of pores, aging was shown to promote pore growth and pore clustering resulting in a complex heterogeneous porous structure. This PhD program will be focused in the one hand on a detailed analysis of the evolution of the mechanical properties with aging (creep, fatigue, adhesion…) and in the other hand on the fine characterization of the 3D nanoporous structure.
The PhD program aims at addressing this issue in order to build thermo-electro-mechanical models allowing anticipating the reliability of the electronic systems.
The PhD program includes :
- Experimental characterization of the thermomechanical behavior
- 3D image analysis of the porous structure and its evolution with ageing
- Finite Element Modeling of the mechanical behavior using representative 3D microstructures identified experimentally
Ideally, the candidate should have notions of basic material science, Finite Element Modelling and 3D image processing.
Net salary is approximately 1360 euros / month – 3 years program from october 1st 2018.
Pour tout renseignement complémentaire, n’hésitez pas à prendre contact :
Email : xavier.milhet@ensma.fr, loic.signor@ensma.fr, pascal.gadaud@ensma.fr
Tél. : 05 49 49 82 09 (Xavier Milhet)